I. Field of the Invention
Embodiments of the present invention relate generally to delivery devices for positioning and deploying vascular devices within a body lumen for treating certain medical conditions. In particular, embodiments are directed to devices and methods for delivering and deploying vascular devices including stents, grafts, and stent-grafts having a low profile in the vasculature of a patient, such as the vessels of the thoracic area.
II. Description of the Related Art
Over the past few decades, advances have been made in the diagnosis and treatment of vascular defects and abnormalities, such as aneurysms, fistulas, lesions, and other conditions affecting a person's blood vessels and/or internal organs. In some cases, conventional braided wire stents and grafts are used to address these conditions in a patient's vasculature. Transluminal prostheses are well known in the medical arts for implantation in blood vessels, biliary ducts, or other similar organs of the living body. These prostheses are commonly known as stents and are used to maintain, open, or dilate tubular strictures or to support tubular structures. When bio-compatible materials are used as a covering or lining for the stent, the prosthesis is called a stent-graft or vascular graft.
An aortic aneurysm, for example, is a weak area in the aorta, which is the main blood vessel that carries blood from the heart to the rest of the body. Weaknesses in the aortic wall may be caused by medical conditions, such as arteriosclerosis. As blood flows through the aorta, the weak vessel wall thins over time and expands like a balloon, which can eventually burst if the vessel wall gets too thin.
Once an aneurysm reaches about 5 cm in diameter, it is usually considered necessary to treat the aneurysm in an effort to prevent it from rupturing. Below 5 cm, the risk of the aneurysm rupturing is lower than the risk of conventional heart surgery in patients with normal surgical risks. The goal of therapy for aneurysms is to prevent the aorta from rupturing. Once an aortic aneurysm has ruptured, the chances of survival are low. Death may be avoided, however, if the aneurysm is detected and treated at an early stage, ideally when the aneurysm is smaller than about 5 cm, using a lower risk procedure.
Aneurysms may be treated with surgery. The surgical procedure for treating some types of aortic aneurysms involves replacing the affected portion of the aorta with a synthetic graft, usually comprising a tube made out of an elastic material with properties very similar to that of a normal, healthy aorta. Surgical treatment is complex, however, and may pose additional risks to the patient, especially the elderly.
More recently, instead of performing surgery to repair an aneurysm, an endovascular stent-graft may be delivered to the site of the aneurysm using elongated catheters. An endovascular stent-graft is a tube that includes a blood-impervious fabric supported by a metal mesh. It can be used to treat a variety of conditions involving blood vessels, but most commonly is used to reinforce a vessel wall at the site of an aneurysm.
To deliver a stent-graft to a target site in a patient's vasculature, typically, the surgeon will make a small incision in the patient's groin area and then insert a delivery catheter or sheath into the vasculature. The delivery sheath usually contains a collapsed, self-expanding or balloon-expandable stent-graft, which is configured to expand to approximately the normal diameter of the aorta at the location of the aneurysm or other abnormality once the stent-graft is deployed from the distal end of the delivery sheath.
The size of the delivery sheath may affect the ability of the surgeon to manipulate the sheath within the patient's vasculature. For example, when the vessel leading to a location of an aneurysm has a diameter that is reduced in size due to arteriosclerosis, larger delivery sheaths may not be used or, at best, may result in trauma to the vascular tissue or may limit treatment options available to some patients. Thus, a smaller delivery sheath may make the treatment available to a larger patient population, lessen the trauma to the vascular tissue, and generally make it easier to accurately deliver and maintain the stent-graft at the proper location. Smaller delivery sheaths also typically allow a physician to access smaller vessels, so as to more proactively treat aneurysms.
For example, a braided, self-expanding stent or a graft incorporating a self-expanding stent as a structural component (referred to herein as a stent-graft) may be introduced into the body by stretching the device axially, until its radial diameter is reduced sufficiently so that it can be fed into a delivery sheath. The device is delivered through the sheath to the site of deployment and then released from the delivery sheath, whereupon the device self-expands to support the patient's vasculature in the location of deployment. A simple delivery device for locating and deploying such a vascular device may include a flexible delivery sheath having a proximal handle and a flexible plunger having a proximal handle. The device is inserted into the distal end of the delivery sheath and the distal end of the delivery sheath is positioned at the site of deployment, such as an artery. The handles of the delivery sheath may be moved relative to each other to push out or uncover the device from the distal end of the sheath.
Because stent-grafts are generally tubular in shape and may lack features at their ends for connecting to a delivery device (such as threads, hooks, etc.), it may be challenging to hold the stent-graft in the contracted state within a delivery device while the delivery device is being positioned at the target site. Likewise, once the delivery device is in position, it may be difficult to deploy the stent-graft from the delivery device or recapture the stent-graft without negatively affecting the configuration of the stent-graft or otherwise impairing the shape or function of the stent-graft.
Accordingly, there is a need for an improved delivery system that provides for a simple and an effective manner of holding a vascular device within the delivery system and allows for the predictable placement of the vascular device within the patient's vasculature, including the ability to reposition or recapture the device prior to full release, such that the shortcomings of conventional solutions are overcome.